The invention relates to a method and a system for determining the wheel position of wheels of a motor vehicle which, for monitoring purposes, in particular for monitoring the tire pressures, are each assigned a wheel unit which transmits data to a central evaluation device of the vehicle, at least in response to a trigger signal.
In conjunction with the systems and the methods of the generic type it is known, for example, that the wheel units transmit information, by means of radio-frequency signals, to a central evaluation device which is arranged on the chassis of the motor vehicle. Wheel unit in the present context is to be understood as any unit which rotates together with a respective wheel and is suitable for supplying information or data which can be used to detect the fault states possibly occurring at the wheel.
The term fault state is to be understood widely in the present context and comprises all states which are considered worthy of detection.
In addition to the actual detection of a fault state, in many systems and methods of the generic type there is provision for the wheel position (for example front left, front right, rear left, rear right) of the individual wheels to be determined so that when a fault state occurs the fault state can be indicated together with the respective wheel position.
For example, EP 0 806 307 B1 has already disclosed a method for carrying out the assignment of the wheel position to air pressure monitoring devices in an air pressure monitoring system of a motor vehicle, the motor vehicle having, inter alia, the following components: a number of wheels, each wheel being assigned an air pressure monitoring device which is capable of transmitting an individual identifier to a central unit, and a central unit in which the assignment of the identifier of an air pressure monitoring device to the wheel position for each wheel is stored. In the method known from EP 0 806 307 B1, the assignment of the air pressure monitoring device to the wheel positions is performed as follows: an assignment mode is switched on; the individual identifiers of the air pressure monitoring device are emitted; which specific identifier has been transmitted from which wheel position is evaluated in the central unit; the determined assignment in the central unit is stored; and the assignment mode is switched off and the air pressure monitoring system is operated in a pressure monitoring mode. In order to evaluate the individual identifiers, there is in particular provision here for a specific variable, for example the wheel speed, to be measured for each wheel of the motor vehicle both with a wheel unit of the pressure monitoring device and with a fixed sensor with a known wheel position. Then, the wheel position of the individual wheels is determined by comparing the output signals of the fixed sensors and the output signals of the wheel units.
DE 197 20 123 C2 has also disclosed that a separate antenna is provided in the region of each wheel to be monitored, it being possible to use said antennas to receive signals emitted by the wheel units. Although each of the antennas can, under certain circumstances, also receive signals of wheel units which are not arranged directly adjacent to the respective antenna, according to the teaching of DE 197 20 123 C2, in order to determine the wheel positions of the individual wheels it is sufficient to assume that a signal which is emitted by a directly adjacent wheel unit and is received has a higher signal level than a signal which is received by the wheel unit which is arranged further away.
The known systems and methods have in common the fact that they are very costly and therefore expensive in terms of the necessary hardware and software.